This invention relates generally to aircraft ejection seats and more particularly to a system for deploying an ejection seat recovery parachute in the most appropriate time sequence for a given set of conditions.
Ejection seat systems generally utilize only two basic parameters in determining the appropriate time sequence for parachute deployment: altitude and airspeed. U.S. Pat. Nos. 4,057,206 to Duncan et al and 3,669,388 to Van Kreuningen, exemplify the current systems.
Additionally, these systems usually have two modes of operation: a low mode and a high mode. The low mode becomes operative when the airspeed is below a certain value (e.g. 225 knots) and/or the altitude is less than a particular value (e.g. 6000 feet). This mode provides optimal timing to parachute extraction under these conditions. The high mode, on the other hand, becomes operative when the airspeed and altitude are greater than the predetermined values. The high mode delays deployment of the parachute by a fixed time period to allow aerodynamic retardation and a reduction in altitude.
The inventors have determined that under certain sink rate conditions a low speed mode provides the best recovery envelope. Under higher sink rate conditions, however, an intermediate mode provides the best recovery envelope. Thus, sink rate can have an effect in optimizing the deployment sequencing mode.